The use of cutting elements comprising an ultra-hard body formed from an ultra-hard material such as diamond, polycrystalline diamond (PCD), thermally-stable polycrystalline diamond (TSP), cubic boron nitride (cBN), polycrystalline cubic boron nitride (PcBN) and the like, that is attached to a substrate formed from metallic or cermet materials is well known in the art. For example, cutting elements that are configured for use with bits for drilling subterranean formations are known to comprise an ultra-hard body that is formed from PCD or TSP and that is attached to a substrate formed from cemented tungsten carbide (WC—Co).
Where the cutting element comprises a PCD body, such is typically attached to the substrate during the high pressure/high temperature (HPHT) process used to sinter the body. Alternatively, the PCD body can be attached to the substrate subsequent to it being sintered by welding or brazing or the like. Where the cutting element comprises a TSP body, the body is typically attached to the substrate, after the diamond body has both been sintered and rendered thermally stable, by welding or brazing process.
A feature that is common to such known cutting elements is the presence of a joint that exists between interfacing surfaces of two materials, i.e., the ultra-hard body and the substrate, that have different elastic and thermal expansion properties. In is well known that the joint in such cutting elements can be subject to large amounts of stress during use of the cutting element caused by the existence of such elastic and thermal expansion property differences between the joined together materials. This stress is known to cause cracking and/or delamination at the joint, between the ultra-hard body and the substrate, that can cause the cutting element to fail, thereby reducing the desired cutting element service life.
Past attempts to address this issue have focused on the entirety of the interfacing surfaces between the ultra-hard body and substrate, and have involved changing the geometry of the interfacing surfaces from having a planar interface to having a nonplanar interface geometry. Such nonplanar interface geometries have generally been achieved by configuring both interfacing surfaces to include one or more complementary surface features that would provide a desired nonplanar interface therebetween.
While such attempts have some effect in reducing some of the stresses existing along the interface between the ultra-hard body and substrate, under certain conditions, it is difficult to make a cutting element with a desired non-planar interface to suppress such stress. For example, it is much more difficult to braze a TSP with non-planar interface to the substrate.
It is, therefore, desired that a cutting element be constructed in a manner that is calculated to reduce and/or eliminate unwanted stresses that can exist at the joint between the ultra-hard body and the substrate, and more specifically, to reduce and/or eliminate the stresses that can exist at the free edge of the interface. It is further desired that such cutting element be constructed in a manner that does not involve exotic materials and/or complex manufacturing techniques.